Wearable exoskeletons have been designed for medical, commercial, and military applications. Medical exoskeletons are designed to help restore a user's mobility. Commercial and military exoskeletons are used to alleviate loads supported by workers or soldiers during strenuous activities, thereby preventing injuries and increasing the strength and stamina of these users.
In powered exoskeletons, exoskeleton control systems prescribe and control trajectories in the joints of an exoskeleton, resulting in the movement of the structure of the exoskeleton and, in some cases, the positioning of a tool supported by the exoskeleton. These control trajectories can be prescribed as position-based, force-based, or a combination of both methodologies, such as those seen in impedance controllers. Position-based control systems can be modified directly through modification of the prescribed positions. Force-based control systems can also be modified directly through modification of the prescribed force profiles. As exoskeleton users vary in proportion, variously adjusted or customized powered exoskeletons will fit each user somewhat differently. The exoskeleton control system should take into account these differences in exoskeleton user proportion, exoskeleton configuration/customization, and exoskeleton user fit to make changes to prescribed exoskeleton trajectories. The exoskeleton user can control changes in exoskeleton trajectories through communication with the exoskeleton control system through a variety of means, including, but not limited to, body pressure sensors, joysticks, touchpads, gestural sensors, voice sensors, and sensors that directly detect nervous system activity.
While the exoskeleton control system assigns trajectories to the joints of a powered exoskeleton and controls the positions of these joints, the actual forces applied to powered exoskeleton joints are exerted by actuators. These actuators can take many forms, as is known in the art, each with advantages and disadvantages in various applications. In current exoskeletons, the actuator exerting force on a joint typically consists of an electric motor located proximal to that joint. Co-location of the actuator with the joint has advantages in terms of mechanical and design simplicity, but it also has certain disadvantages. Foremost among these disadvantages is that adding a bulky electric motor to a joint increases the bulk of the joint, limiting maneuverability of the joint and exoskeleton in certain environments. In comparison, consider a human finger: the musculature exerting force on the joints of the finger is not located near the joints of the finger but rather in the forearm, with muscular contraction pulling on tendons that relay that force over distance to the joints. This has the advantage of minimizing the bulk of the fingers, allowing for both greater dexterity and closer placement of the fingers to each other. In addition, more muscle can be located in the arm than would fit on the fingers, allowing for greater strength. One mechanical actuation device, described in U.S. Pat. No. 4,843,921, uses a drive mechanism in which an electric motor twists on a loop of cord, with this cord loop forming a helical structure and shortening as it is twisted, pulling the two ends of the cord loop closer together. In this way, activation of the electric motor is used to apply a pulling force over distance through the cord loop. This allows for a design in which the motor driving the movement of a joint is located at a position distal to the joint.
Modern soldiers bring a large amount of weight with them into combat operations, including equipment, munitions, and body armor. In recent conflicts, American infantrymen have actually carried more weight than what was borne by fully-armored and armed medieval knights. This increase in carried weight has led to a number of problems, including reduced speed and increased risk of injury (including knee and back injuries), as well as difficulty standing from a prone position, climbing over objects, and dismounting from a vehicle. Exoskeleton devices, both powered and unpowered, have helped address issues relating to walking with increased weight—allowing greater carrying capacity and reducing risk of injury. However, increasing strength in the arms has been complicated by a number of factors, including the complexity of the human shoulder and wrist joints as well as the need for substantial arm dexterity in combat that would be impeded by bulky actuators affixed to the arms and shoulders. Further, heavy robotic arms would only add to the weight of a soldier (and exoskeleton), resulting in additional problems including tradeoffs relating to energy consumption and speed.
In view of the above, there exists an unmet need to provide a device that allows an exoskeleton to power the movements of the human arm, with this device providing power in such a way as to not restrict the fine motions at the shoulder. There further exists an unmet need for a device powering the movements of the human arm that does not limit arm dexterity and, more specifically, for a device that does not add substantial weight or bulk to the arms.